The Bakrie brothers have broadened their campaign against the troubled coal miner they helped set up with financier Nat Rothschild, saying the “Bumi affair” had damaged London’s reputation with emerging market investors.

Bumi has been riven with conflict since it was created in November 2010 when the Bakries reversed some of their Indonesian coal mining assets into financier Nat Rothschild’s London-listed cash shell.

The Takeover Panel ruled in December that there had been improper disclosure about the relationship between two key shareholders, the Bakrie brothers and Rosan Roeslani, and that they had been acting “in concert”.

As a result, the panel ordered that the voting power of their combined 57% stake be cut almost in half. It is now investigating why the concert party was not brought to its attention at the time of the reverse takeover.

“We respectfully ask that the panel move rapidly with what is... one of the most serious inquiries it has undertaken,” Bakrie Group’s Nirwan Bakrie said. “Shareholder votes at Bumi have been massively distorted to the disadvantage of Indonesian shareholders.”

“And the panel was kept in the dark about key facts at the time of the creation of Bumi. How this occurred goes to the heart of why the structure has been so disappointing and also done serious damage to London’s reputation as an honest capital market with emerging market investors such as ourselves,” Bakrie added.

The Bakries blame Rothschild for failing to disclose the relationship to the panel when he did the deal, arguing he has created a situation that has left them at a disadvantage.

Under the takeover code, any person - or persons acting in concert - owning a stake of 30% or more in a company must launch a bid for the whole business, unless the panel approves a waiver. Had the Takeover Panel been made adequately aware of the facts and ruled that there was a concert party, as it has now, we would certainly have sought a waiver, the Bakries said in December.

A Rothschild spokesman said the Bakries’ statement showed “the desperate attempts by the concert party and its allies to retain control of Bumi”.